A major breakthrough in the large scale cultivation of algae and cyanobacteria to produce commercially useful products was the discovery that many such species could be cultivated with flue gas (up to 80% CO2) or even pure CO2 whereas most other organisms (plants and animals) are “biochemically anaesthetized” at CO2 levels of 5% or higher, slowing all metabolism. This opened the way for cultivating such organisms on CO2 emissions to the environment (Murakami and Ikenouchi 1997, Negoro, et al. 1993).
Cyanobacteria have already begun to be genetically engineered to utilize these elevated CO2 levels by over expressing genes encoding rate limiting enzymes of the “dark reactions” (CO2 assimilating reactions that utilize NADPH and ATP from the light reactions) of photosynthesis. Thus, for example, engineering genes from rice encoding for cytosolic fructose-1,6-bisphosphate aldolase and spinach triose phosphate isomerase in cells of a cyanobacterium doubled their activities and greatly increased photosynthetic efficiency and biomass yields (Kang et al. 2005, Ma et al. 2007).
However, one can only over-express enzymes to a limited extent, as the cell does not have unlimited capacity. Therefore, the existing methods have only a limited capacity and there is a need to improve these methods to enhance the use of elevated carbon dioxide concentration in algal cultures.